Implementation Methodology and Testbed

We have implemented the proposed kernel mechanisms in AIX 5.0, and evaluated them on the testbed described below. As shown in Figure 4, the QoS module contains the TCP SYN policer, a priority assignment function for new connections, and the entity that performs URL-based admission control and priority assignment.

All experiments were conducted on a testbed comprising an IBM HTTP Server running on a 375 MHz RS/6000 machine with 512 MB memory, several 550 MHz Pentium III clients running Linux, and one 166 MHz Pentium Pro client running FreeBSD. The server and clients are connected via a 100 BaseT Ethernet switch. For client load generators we use Webstone 2.5 [15] and a slightly modified version of sclient [16]. Both programs measure client throughput in connections per second. The experimental workload consists of static and dynamic requests. The dynamic files are minor modifications of standard Webstone CGI files that simulate memory consumption of real-world CGIs.

The IBM HTTP Server is a modified Apache [17] 1.3.12 web server that utilizes an in-kernel HTTP get engine called the Advanced Fast Path Architecture (AFPA). We use AFPA in our architecture only to perform the URL parsing and have disabled any caching when measuring throughput results. Unless stated otherwise, we configured Apache to use a maximum of 150 server processes.